The present invention relates to the technical field of implantable vertebral arthrodesis devices for fusing together an overlying vertebra and an underlying vertebra.
The term “arthrodesis” is used to cover any fusing of a joint. Such implantable devices serve to distribute loads and overloads between two adjacent vertebrae (referred to herein as the overlying and the underlying vertebrae) as occurs as a result of degeneration of a disk (in particular in the event of a herniated disk). By way of example, in the event of degenerative disk disease, a stress or a lesion can lead to the disk tearing or to a protuberance forming, possibly leading to contact with and compression of a spinal nerve root. Contact with a nerve can lead to intermittent lumbago.
One method of treating this type of disease consists in immobilizing the over- and underlying vertebrae by bone fusion while re-establishing the distance between the spinous processes and the lordosis angle of said vertebrae.
The implantable devices that are in the most widespread use in this method of surgical treatment comprise two rods connected to the over- and underlying vertebrae via screws positioned in the pedicles, with an osteosynthesis graft being applied to the vertebrae, the graft being positioned on the external portions of the screws and the rods.
That type of implantable device requires a large operating field to be opened, giving rise to necrosis in surrounding tissues of the patient that are handled in order to gain access to the pedicles and in order to put the screws and the graft into place.
Furthermore, the fastening points on the pedicles, using pedicular screws, are far away from the vertebral bodies on which the greatest loads are exerted. That configuration leads to a large lever arm, and thus to a transfer of the load applied initially to the pedicular screws, which can lead to them breaking. In order to remedy that drawback, and depending on the state of degeneration of the disk, those devices also have one or two inter-somatic cages inserted via the posterior, lateral, or anterior approach, thereby increasing the duration of surgery and thus increasing risks for the patient.
It has been found that the bone graft arranged in such cages shrinks in volume after being implanted, with the shrinkage being in particular by about 20%. Unfortunately, it is necessary for the bone graft to be mechanically stimulated by the vertebral bodies between which it is in contact in order for arthrodesis to be able to develop properly. With a rigid inter-somatic cage, it is therefore necessary to fill it with graft so that the bone graft projects beyond the ends of the cage. That configuration can make it more complicated to adjust lordosis and the distance between vertebrae.
WO 2013/123497 relates to an inter-spinous fusion device comprising a central body portion that is defined between first and second opposite lower walls, a rear wall, and first and second upper walls. The central body portion is open to its posterior portion, and can receive a graft only in the form of a solid block.
US 2012/0215262 relates to an osteosynthesis device for placing between the spinous processes. That device does not make it possible to achieve fusion between laminae.
U.S. Pat. No. 8,292,923 B1 relates to an implant for placing between the spinous processes. That implant likewise does not provide bearing between laminae and cannot be used to achieve fusion between laminae. In addition, it is not arranged to receive the spinous processes, at least in part. The central cavity occupies only a few millimeters and merely makes surface contact with the spinous processes.
There exists a need for a vertebral arthrodesis device for fusing together two adjacent vertebrae, in particular in the lumbar region, in particular for treating degenerative or accidental disk disease, but without requiring the use of screws and rods, so as to be able to reduce the operating field on the patient, thereby serving to diminish necrosis of the tissue surrounding the site of implantation.
There also exists a need for a vertebral arthrodesis device that enables the distance between the vertebrae and the lordosis angle between the overlying and underlying vertebrae to be adjusted in the vertebral region that is to be corrected.